Polyamide for Flexible Packaging Film

2003 PLACE Conference 12 – 14 May 2003 Rome, Italy

Dr. Walter Goetz, BASF AG, Ludwigshafen/Germany

Abstract

PA 6 is a widely used resin for the production of flexible packaging film, in most cases combined with polyolefins as a component of a multilayer structure. It has found numerous applications for its unique combination of properties like mechanical strength, transparency, thermoformability and barrier. This presentation summarizes the fundamental information about the chemistry and properties of nylon resins, their processing, and the properties and applications of packaging film produced utilizing nylon. Polyamides may be processed into film by blown or cast film process, oriented or non-oriented. Standard extrusion equipment may be used, however post-treatment by humdidification or annealing helps to postcrystallize PA film and to achieve dimensionally stable, ready-to-use film of high quality.

Polyamide for Flexible Packaging Film fig 1

1. Introduction

Polyamide is widely used for the the production of flexible film for packaging of perishable food due to its unique combination of properties: fig 2: z mechanical strength

z high heat distortion temperature

z high flexibility and toughness

z good barrier to oxygen, chemicals and aroma substances

z high transparency

z thermoformability

fig 3 In 2002, about 260 000 t of polyamides, mainly PA 6 and copolyamides PA6/66, were used for packaging film worldwide. Multilayer films in combination with PE, PP or EVOH form the major share of the polyamide film market. fig 4 The term “polyamide” describes a family of polymers which are characterized by the presence of amide groups. Since the first - and still most important - synthetic polyamides, PA66 (Nylon) and PA6 (Perlon), have been developed in 1938/39, they have found wide applications as film, fibers, engineering resins and others. Today, DuPont”s original brand name for PA66, “Nylon”, is often used as generic name for all synthetic polyamides. However, polyamides have been useful materials long before the development of these synthetic nylon resins as the naturally occuring protein, the polymer of α-aminoacid, the base material of wool and silk, is also to be considered a member of the polyamide group.

2. Chemistry and Properties of Polyamide Resins fig 5 Polyamides are mostly aliphatic, linear polymers characterized by the presence of the amide group, the condensation product of amine and carboxylic acid, as repeating unit in the polymer chain, separated by hydrocarbon unit. fig 6 Polyamides may be synthesized either by (A) polycondensation of divalent carboxylic acid and divalent amines, or by (B) polycondensation of difunctional aminoacids containing both one amine and one carboxylic acid functionality in the same molecule (or their intramolecular ring-shaped condensation products "lactams"). The many different types of polyamides are named according ISO 1874 by the using symbol PA (for polyamide) and: fig 7 - (A) the number of carbon atoms in the diamine monomer, followed by number of carbon atoms in the dicarboxylic acid (for linear aliphatic polyamides), e.g. PA 66 for the polyamide of hexene diamine and adipic acid or PA612 for the polyamide of hexene diamine and dodecanic diacid, or - (B) the number of carbon atoms in the aminoacid or lactam monomer (for linear aliphatic polyamides), e.g. PA 6 for the polyamide of caprolactam (aminocaproic acid) or PA12 for the polyamide of laurine lactam

Other monomers are indicated by letters defined in ISO 1874, e.g. I for isophthalic acid or T for terephthalic acid. Copolyamides are designated by listing their monomers separated by a slash, e.g. PA 6/66 for the copolymer of caprolactam, hexene diamine and adipic acid.

Many technically used synthetic polyamides are derived from monomers containing 6-12 carbon atoms; most prevalent are PA6 and PA66. The film sector is dominated by PA6 and the random copolymer PA6/66, mostly due to their relatively easy processing that facilitates coextrusion with lower melting, thermally sensitive polyolefins. fig 8: important polyamides type monomers melting water absorption temperature (in water, 23°C) PA66 A hexene diamine (C6) 260°C 8.5% adipic acid (C6) PA 610 A hexene diamine (C6) 220°C 3.3% sebacic acid (C10) PA 612 A hexene diamine (C6) 215°C 2.8% dodecanic diacid (C12) PA 6 B caprolactam (C6) 220°C 9.5% PA 11 B aminoundecanic acid (C11) 185°C 1.8% PA 12 B aminododecanic acid (C12) 178°C 1.5% PA 6/66 A,B copolyamide of caprolactam (85%), hexene 195°C 10.5% (85:15) diamine and adipic acid (15%) PA 6I/6T A hexene diamine (C6) Tg = 132°C *) 1.3% Terephthalic and Isophtalic acid *) glass transition temperature

The amide groups in the mostly semicrystalline polyamides are capable of forming strong electrostatic forces between the -NH and the -CO - units (hydrogen bonds), producing high melting points, exceptional strength and stiffness, high barrier properties and excellent chemical resistance. However, the amide units also form strong interactions with water, causing the polyamides to absorb water in a range between 2 and 20%. These water molecules are inserted into the hydrogen bonds, loosening the intermolecular attracting forces and acting as a plastisizer, resulting in the exceptional toughness and elasticity well known of polyamides.

3. Film Processing of Polyamide Resins

3.1. Pre-Processing

Polyamide, as a water absorbing polycondensation polymer, is sensitive to moisture. Processing nylon resin with excessive moisture content will result in molecular weight degradation by hydrolysis and the formation of steam bubbles. To prevent this, the moisture levels should be maintained below 0.1 wt%. Most resin producers supply nylon pre-dried and in moisture-proof packaging to ensure the resin stays dry and ready for use. Once this moisture proof packaging is opened, nylon will begin absorbing moisture from the atmosphere, therefore nylon exposure to air humidity after opening the bag must be minimized by rapidly using the resin or by blanketing the resin with dry air or nitrogen. This action is essential for bulk supply of polyamide resin which is of rapidly increasing importance. fig 9

Only if a polyamide resin absorbs more than the recommended 0.1 wt.%, it should be dried at 80°C utilizing a dry air dryer of dew point below –20°C. Simple hot-air dryers should be avoided as they may actually humidify nylon when ambient humidity levels are high.

3.2. Extrusion

Polyamide can be processed as blown and cast film, and can be used for extrusion coating and the procution of biaxially oriented film (BOPA).

Polyamide processes well in a wide variety of standard extrusion equipment. General recommendations for an extruder to process nylon are: fig 10: • barrier or 3-zone compression screw • compression ratio between 3.1:1 and 4:1 • length to diameter (L/D) ratio at least 24:1 or higher • 35% feed (preheating) • 15% compression (melting) • 50% metering (homogenizing)

Polyamides melt at relatively high temperatures and need higher processing temperature than polyolefins. A typical temperature profile for a screw with 5 heat zones for processing polyamide 6 would be (for copolyamide PA6/66, 20°C lower temperatures): fig 11: barrel film throat zone zone zone zone connecting head melt type type 1 2 3 4 pipe [°C] temperature [°C] [°C] [°C] [°C] [°C] [°C] smooth blown 200 260 258 253 250 250 250 250 gooved blown 200 240 243 247 250 250 250 250 smooth cast 200 275 272 268 265 265 265 265 grooved cast 200 260 255 260 265 265 265 265

3.3. Film Forming

Polyamide is used in both cast and blown film equipment, predominantly for multilayer films. Since nylon is a semicrystalline material, processes that rapidly cool the polyamide film will result in lower crystallinity and therefore provide more transparent, flexible, thermoformable film. fig 12

crystallisation rate of PA6

1 0.1

0.01 0.001

[1/sec] 0.0001

crystallisation rate 0.00001 50 150 250

crystallisation temperature [°C]

For cast films, standard equipment as used for PE or PP is used for multilayer film with polamide layers. Factors to consider are fig 13: • chill roll temperature 20-50°C for high thermoformability • chill roll temperature 75-85°C for high dimensional stability • polyamide resins with viscosity number 200-230 cm³/g • polyethylene resins of MI = 3.0 – 4.0 cm³/10min

Standard blown film equipment is used for producing multilayer films with nylon layers. In general, these topics need to be considered for blown film fig 14: • Cooling with ambient air or refrigerated air • optional IBC Internal Bubble Cooling • Blow up ratio: 1:1.1 – 1:2.5 • Polyamide with Viscosity Number 200-260 cm³/g o predominantly random copolyamides PA6/66 • Polyethylene of MI = 0.8 – 1.0 cm²/10min

A technology already published in the literature in the late 50’s but that attracted more attention recently is the extrusion of a tubular film into a cold-water bath, optionally with internal water cooling mandrill. This film forming method provides extremely high cooling rates and produces therefore – even at high specific output - film of even better transparency and thermoformability than rapidly cooled cast film. On the other hand, this tubular film avoids some of the disadvantages of cast multilayer film such as difficult to control layer distribution and hardly recyclable edge trim of significant amount. fig 15

Biaxially oriented PA film (BOPA) may be produced by both blown film process ("double bubble") and cast film ("tenter frame ") process with simultaneous or sequential orientation, similar to those used for BOPET and BOPP. fig 16

The production of biaxially oriented nylon film consists of the consecutive steps:

• extrusion of a rapidly quenched, amorphous primary film • reheating of the primary film • stretching • thermofixation/annealing

For some applications such as shrink bags or sausage casing, a controlled level of shrinkability is retained in the film by only partly annealing the film. Such sausage casing film – which has a double function as processing aid for curing the sausage but also as packaging film – is today produced by double bubble BOPA process with up to seven layers of PA, PE and optionally EVOH. fig 17

3.4. Post-Treatment

A specific property of polyamide, that makes it distinct of most other polymers, is its water absorption fig 18

When nylon exits the extruder, it will absorb moisture from the atmosphere over time. The absorbed water acts as a plasticizer and lowers the glass transition temperature. fig 19

This effect drastically increases the elastic properties of polyamide film such as

• flexibility • elongation at break • puncture resistance • impact strength • thermoformability fig 20 Polyamide film should therefore be used or converted only after it has been conditioned with water. This may be done by giving the film sufficient time to come to equilibrium with the air humidity – a process which may consume considerable time especially in case of multilayer film where a PA core layer is embedded in polyolefin skin layers. A ready-to-use film may be obtained by in-line humidification by passing the film through a hot-water bath, a steam chamber or a water-spray station.

fig 21 An additional benefit of in-line humidification is the high dimensional stability of film produced utilizing such equipment. Polyamide is a semicrystalline material that crystallizes more or less completely, depending on the type of polyamide and the cooling rate during the film solidification: Rapidly quenched film made by cast film process with very low chill roll temperature or water-cooled blown film is nearly amorphous, whereas blown film cooled with ambient air is highly crystalline. Amorphous or partly crystallized film will postcrystallize and shrink when the film absorbs humidity from the air. Cutting to the desired film width can therefore only be completed once the film is conditioned. By in-line humidification, or even by only in-line reheating to a temperature above the glass transition temperature, the film will immediately postcrystallize and complete its shrinkage process. Such a film can be cut to the desired width immediately without prior conditioning time. This effect was demonstrated by producing a monolayer (50µm) film at 20°C chill roll temperature, the crystallinity of this film (according X-ray scattering) was < 1%. Within 2h of exposure to 23°C/65% rh, this film was shrinking 1-2%. But if the film had passed a second, heated “chill” roll of 80-100°C during the extrusion process, the film remained at its original dimensions when exposed to humid air. fig 22

The reason for this shrinkage is a solid-state postcrystallisation of the initially amorphous film as soon as the temperature exceeds the polyamide’s glass transition temperature (55°C), or as soon as the absorbed humidity from the air causes the Tg to drop below the ambient temperature. However this postcrystallisation does not affect the beneficial properties that make rapidly cooled film superior to slowly cooled, highly crystalline film:

high transparency high flexibility superior puncture and impact resistance good thermoformability fig 23

If film is cooled slowly, it has sufficient time to grow crystals of significant size, spherulites. These scatter and reflect visible light and cause haze – however the addition of a nucleating agent into the PA resin will help to reduce the spherolite size to below 400nm, the wavelength of the visible light, and significantly improve transparency. SEM micrographs show that the spherulites are agglomerates of microcrystals. fig 24

Rapidly cooled film is optically transparent, however SEM micrographs reveal the same type of microcrystals – after postcrystallisation by exposing the film to humidity. But the microcrystals produced by solid-state postcrystallisation do not agglomerate to form large, visible spherulites.

4. Properties of nylon film Nylon properties are dominated by the presence of the amide group in the polymer chain, which provides strong intermolecular adhesion via hydrogen bonds. These strong attractive forces between the molecules result in fig 25 • high melting point and heat resistance • high mechanical properties (strength, stiffness) • high barrier to oxygen, carbon dioxide and many solvents and aroma materials

The highly polarity of the amide groups is also responsible for the water absorption of nylon resins. Water molecules inserted into the hydrogen bonds provide superior elastic properties, as fig 26 • high puncture resistance and toughness • good thermoformability

The outstanding feature of nylon is the fact that it provides all these properties simultaneously to the film construction. Nylon is therefore chosen when a complex property portfolio is requested from a film construction.

4.1. Mechanical Properties Nylon shows exceptionally high strength, toughness and puncture resistance and provides these properties also to multilayer film based on nylon. As the mechanical properties of nylon film depend on the resin's water absorption. Water acts as a plasticizer for polyamides, lowering its strength and stiffness while increasing its toughness, drawability and elasticity. As film rapidly absorbs moisture – surface layers within minutes, but even PA layers shielded by polyethylene layers from the ambient atmosphere within a few days – only mechanical properties after moisturization into humidity equilibrium are relevant.

4.2. Barrier Properties fig 27 PA6 has an intermediate oxygen transmission rate (OTR) that increases at higher humidity levels. Its barrier is 2 magnitudes higher than that of polyolefins, but still 10-100x inferior to high-barrier EVOH. In high humidity eviroment, the EVOH’s barrier is reduced even stronger and may achieve the magnitude of special polyamide resins as PA MXD6, the polyamide of m-xylylene diamine and adipic acid.

Nylon shows superior barrier to chemicals of low polarity as hydrocarbon solvents, but also to low polarity aroma substances in food component, as limonene, campher, vanillin and menthol. Only with regard to highly polar chemicals that are readily absorbed by nylon, as water, ethanol or methanol, its barrier is is inferior. fig 28: barrier of various polymer resins, at 23°C, for 25µm film thickness (typical values) N2 CO2 C2H6 H2O Isooctane limonene Menthol 25µm film 0% rh 0%rh 85→0% 50%rh 50%rh 50%rh cm³/ cm³/ cm³/ g/m² d g/m² d g/m² d g/m² d m²d bar m²d bar m²d bar PA6 14 200 0.5 35 0.08 0.012 <0.01 BOPA6 12 150 0.4 30 LDPE 5 350 60 10 EVOH 0.1 0.012 <0.01 44%

4.3. Thermoformability fig 29 Polyamide is often used in multilayer structures for its high maximum deep draw depth and its ability to maintain as much barrier layer thickness in the corners of the thermoformed, the areas of deepest draw. fig 30 In a multilayer film PE-tie-PA-EVOH-PA, the EVOH’s drawability is significantly improved compared to a structure where the EVOH barrier layer is not sandwiched between PA layers.

4.4. Sealability fig 31 An outside layer of PA provides high heat resistance to a multilayer film structure, allowing the processor to operate at a high sealing bar temperature without sticking of the film to the sealing bar surface. Such a film will therefore provide high sealing line speed as well as good seal quality. For this type of film, a well crystallized PA film – by slow cooling or solid-state postcrystallisation – is essential to avoid shrinkage of the film in the seal area, which might result in wrinkles and pinholes.

4.5. Properties of Oriented PA Film fig 32 Biaxially oriented nylon (BOPA) film is characterized by

• very high stiffness • very good printability • very high strength • high puncture resistance • low elongation to break

Its deformation mode under load is dominated by an elastic behavior, rather than the plastic deformation of standard nylon film. Biaxially oriented nylon film is therefore highly suitable for metallisation or coating with inorganic barrier layers as “SiOx”, further it exhibits very good printability due to its high dimensional stability under load. fig 33

BOPA has a 30% higher oxygen barrier compared to non-oriented cast PA film, a small increase compared to the 3x improvement between BOPET and non-oriented CPET. This is caused by the fact that in case of PA, BOPA film with its stress-induced crystallinity is compared to crystalline CPA film, whereas in case of PET film, the non-oriented baseline is formed by a predominantly amorphous CPET film.

5. Applications fig 34, fig 35 The wide majority of nylon film is used as a component of coextruded or laminated mulitlayer film for packaging of food sensitive to oxygen, such as • meat • processed meat (sausage, bacon) • smoked fish • cereals • cheese and diary products • semi-finished meals ("TV dinner")

BASF Aktiengesellschaft, Performance Polymers

NylonNylon forfor FlexibleFlexible PackagingPackaging FilmFilm Dr. Walter Goetz BASF AG, Ludwigshafen/Germany

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 1 Polyamides are widely used for demanding applications in the packaging field for due to their unique combination of mechanical strength high heat distortion temperature high flexibility and toughness good barrier to oxygen, chemicals and aroma substances high transparency thermoformability

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 2 PA consumption for film production

Asia Europe PA others 35% 35% 6/66 4% 13%

PA 6 83%

America 30% total: 260 kt (2002)

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 3 Introduction: What are Polyamides? zSynthetic Polyamides were developped in 1938  Perlon, Polyamid PA6 in Germany  Nylon, Polyamid PA66 in USA z naturally occuring polyamides are proteins silk, wool, .. z First applications for fibers, later also for engineering resins and for packaging film ztoday, Nylon is often used as generic name for PA

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 4 Introduction: What are Polyamides? zPolyamide properties dominated by amide group H I -C-N- II strong interaction O with each other H I with water -C-N- II O zbetween amide groups, water-repellent hydrocarbons are located

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 5 Introduction: What are Polyamides? polyamides may be synthethized from

type A: di-acid + di-amine

A A N N

type B: aminoacid N = Amine group N A A = Acid group

= hydrocarbon block

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 6 Introduction: Nomenclature of Polyamides type A: PA (number of amine carbon atoms) (number of acid carbon atoms)

N--CH2-CH2-CH2-CH2-CH2-CH2-N-C--CH2-CH2-CH2-CH2-C-N- H H O O H

type B PA (number of aminoacid carbon atoms)

N-C--CH2-CH2-CH2-CH2-N-C--CH2-CH2-CH2-CH2-CH2-N-C- H O H O H O

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 7 important Polyamides monomers Tm water absorption PA 66 hexene diamine, adipic acid 260 °C 8.5% PA 612 hexene diamine, dodecanic diacid 215 °C 2.8% PA 6 caprolactame (aminocaproic acid) 220 °C 9.5% PA 12 laurinlactame 178°C 1.5% PA 6/66 hexene diamine, adipic acid 195°C 10.5% (85:15) caprolactame PA hexene diamine, isophthalic acid, Tg = 1.3% 6I/6T terephthalic acid 132°C

PA6 and PA6/66 most important for packaging film

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 8 moisture absorption rate of PA 6 PA typically pre- 0.2 dried keep under dry-air blanket drying only with dry- 0.1 Maximum air dryer recommended

humidity [%] humidity moisture for processing

0 0 30 60 90 120 150 exposure time to 23°C/65° rh [min]

Moisture absorption of a single pellet layer, 65% r.h. / 23°C

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 9 ProcessingProcessing ofof PAPA :: GeneralGeneral RecommendationsRecommendations

z barrier or 3-zone screw z minimum length/diameter of barrel (L/D) 24:1 z compression ratio 3:1(PA6) Feed 35 % 9 D Compression 15 % 4 D Metering 50 % 11 D

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 10 ProcessingProcessing ofof PAPA :: TemperatureTemperature ProfileProfile 280

260

240 smooth barrel - blown film [°C] grooved barrel - blown film

220 smooth barrel - cast film

grooved barrel - cast film 200

3 ad e e 1 e 2 e ur he throat on on rat z z zon zone 4 e

connecting mp te elt PA6/66: 20°C lower temperature profile m

examples for typical temperature profile Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 11 ProcessingProcessing ofof PAPA :: CrystallisationCrystallisation RateRate ofof PA6PA6 180 – 130°C: crystallisation rate of PA6 moderte crystallisation rate 1 < 80°C: 0.1 crystallistion frozen 0.01 0.001 rapid cooling: [1/sec] 0.0001 amorphous film

crystallisation rate 0.00001 slow cooling: 50 150 250 crystalline film crystallisation temperature [°C]

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 12 Processing of Polyamide film: Cast Film

standard cast film equipment chill roll 70-85°C : dimensional stability chill roll 20-35°C: high thermoformability

PE (MI = 3-4) PA6 (RV3,2-3,6) nucleated PA recommended

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 13 Processing of Polyamide Film: Blown Film

standard blown film equipment air or refrigerataed air cooling optional IBC

PE (MI = 0.8 – 1 cm³/10min) + co-PA 6/66 (RV 3.2-3.6) + PA6 (RV 3.8-4.0)

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 14 Processing of PA Film: Water-Quenched Blown Film superior vacuum thermoformability high puncture vacuum resistance high line speed no/little edge trim

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 15 Processing of PA Film: Biaxially Oriented PA Film

reheating BOPA film:

stretching rapid cooling cooling reheating >Tg stretching thermofixation annealing/ thermofixation double bubble process tenter frame - simultaneous tenter frame - sequential

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 16 BOPA Sausage Casing

double bubble process monolayer / multilayer defined shrinkability oxygen barrier meat (protein) adhesion printability

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 17 Moisture Absorption of PA 6 Film C=O H-N

2.5 H-N C=O

2 humidity 1.5

1 C=O H-O H-N moisture [%] H 0.5 H-N C=O

0 0 20406080 time [min] moisture absorption of a 50µm PA6 mopnolayer film; 23°C / 65% r.h. Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 18 Moisture Absorption of PA 6 Film water 60 ƒ inserted into 50 hydrogen bond 40 ƒ plasticizer 30 ƒ lowers Tg 20

Tg [°C] 10 + flexibility 0 + puncture -10 resistance -20 + thermoformability 0246810 water content [%] glass transition temperature of 1mm PA6 plates, torsion pendulum Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 19 Post-Treatment: In-line Humidification

Water bath 45-80°C

55-65°C

extruder for blown or cast film water tank or steam tunnel film immediately ready to use no postshrinkage curl reduction of non-symmetric blown film Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 20 Post-Treatment: Dimensional Stability

340 in-line postcrystallized rapidly cooled film: 339 ⇒shrinkage by water 338 absorption 337

film width [mm] width film 336 no post-treatment in-line humidification or annealing: 335 0 50 100 150 ⇒ no further shrinkage exposure time to 65% r.h. [min]

dimensions of 50µm single layer PA6 film, 20°C chill roll temp Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 21 Post-Treatment: Solid-State Postcrystallisation

40 35 solid state 30 postcrystallisation by 25 20 ƒ temperature 15 23°C 10 35°C (T > Tg) 5 52°C % crystallinity [DSC] crystallinity % 0 ƒ humidity 0204060 exposure time to 100% r.h. (Tg < T) X-ray: <1% postcrystallisation of 50µm single layer PA6 film (20°C chill roll temp) at 100% rh Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 22 Post-Treatment: Solid-State Postcrystallisation 1:640x / light 1:10 000x / TEM 1:212 500x / TEM

ƒ visible crystallinity = spherulites ⇒ agglomerates of microcrystals

crystallinity of 50µm single layer film (130°C chill roll temp); nucleated PA6

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 23 Post-Treatment: Solid-State Postcrystallisation 1:640x / light 1:212 500x / TEM crystalline film: ƒspherulites slowly cooled ƒagglomerates of microcrystals X-ray: 34% cryst. „amorphous“ film: ƒno spherulites rapidly cooled ƒmicrocrystallinity by post- X-ray: crystallisation 25% cryst crystallinity of 50µm single layer PA6 cast film (130°C and 20°C chill roll temp)

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 24 Properties of Polyamides amide-amide interactions provide ƒhigh melting point C=O H-N ƒhigh strength H-N C=O ƒhigh stiffness ƒgood abrasion resistance ƒhigh barrier/resistance to chemicals gasoline, fat, aroma materials..... ƒHigh oxygen barrier ƒgood printability ƒwater absorption

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 25 Properties of Polyamides amide-water interactions provide

ƒflexibility and elasticity C=O H-O H-N ƒhigh toughness H-N H C=O ƒhigh stiffness ƒgood thermoformability ⇒ only after water absorption

zpolyamide have simultaneously advantages in all these properties

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 26 Properties of Polyamide Film: Barrier Properties

1000 PE PP zhigh oxygen barrier of PA6

100 PA 6 zsome aromatic polymers PET 10 PA 6I/6T with even higher barrier PA MXD6 1 PVDC zEVOH very high barrier,

EVOH (44 mol%) but strong reduction at high 0.1 EVOH (32 mol%) humidity

0.01 0 20406080100 oxygen permeabilityt [ml 100µm / m² d bar] 100µm / [ml permeabilityt oxygen relative humidity [%]

Oxygen barrier for 100 µm of various packaging polymers

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 27 Properties of PA Film: Solvent and Aroma Barrier z very high barrier to 1000 PA6 EVOH PE low polarity

100 chemicals and aroma substances 10 z high barrier to 1 intermediate polarity chemicals P25 [g 25µm / m² d] / m² 25µm [g P25 0.1 z exceeds barrier of 0.01 PE by magnitudes butyl (60°C) vanillin (60°C) (60°C) acetate menthol acetone campher limonene z no barrier to water isooctane isopropanol and alcohols

Permeation rate P25 for different solvent molecules at 23°C / 25µm PA6

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 28 Thermoforming of Polyamide Film

thermoforming depth PE

Adhesive PA

PE tie PAPA EVOH PA thinnest spots thinnest spots

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 29 Properties of PA Film: Thermoforming

100 PA6 (Ultramid B36FN) 90 EVOH (44mol%) 80 70 PA6/EVOH/PA6 60 50 40 30 20

residual wall thickness [%] thickness wall residual 10 0 Folie 10mm 20mm 40mm 60mm thermoforming depth [mm] residual wall thickness [% of initial thickness of barrier layer] of blown film PE/adh/PA(50µm)/adh/PE PE/adh/EVOH(10µm)/adh/PE PE/adh/PA(20)/EVOH(8)/PA(25) thermoforming 120x80mm, 6mm corner radius, 90°C Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 30 Properties of PA Film: Heat Resistance Tm [°C]

PA HDPE 130-135 tie PE PE LDPE, 110-125 tie PA LLDPE PP 165 PA6 220 PA skin layer: PA66 260 *) z high sealing temperature PET 260 *)

z no sticking to sealing bar *) processing temperature too high for coextrusion z rapid sealing

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 31 Properties of BOPA Film stress

elastic deformation 500 CPET BOPET 400 break CPA plastic deformation 300 BOPA yield point strain 200

100 stiffness printability 0 metallizable Modulus Strength Dart OTR [0.1 MPa] [MPa] Drop [cm³/m² d puncture [10 Nm] bar] resistance

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 32 Properties of BOPA Film oriented film:

180 crystalline 160 stress-induced 140 crystallisation cast 120 cast-fresh 100 biax oriented 80 cast film 60 CPET: amorphous 40 CPA: crystalline 20 0 PET PA

OTR (0% rh) of 25µm film, cast / cast-dry as moulded / biaxially oriented

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 33 Applications

Polyamides is used for packaging film for its mechanical strength and toughness high temperature resistance good barrier thermoformability mostly for packaging of oxygen-sensitive food as meat and processed meat cheese processed food

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 34 Applications

Nylon for Flexible Packaging Film TAPPI Rome 5/2003 Dr Walter Goetz 35 TAPPI 2003 European PLACE Conference Rome, May 12 - 14, 2003

AdhesionAdhesion ofof AluminiumAluminium FoilFoil toto CoatingsCoatings -- StickStick WithWith ItIt !!

Günter Schubert, Hydro Aluminium Deutschland GmbH, Bonn

TAPPI 03 / G. Schubert 14.05.2003

Structure

 Manufacturing Aluminium Foil  Formation and Composition of Aluminium Foil Surface  Cases challenging adhesion lacquered and extrusion-coated dairy lidding adhesive laminates and retorting sealant - packaged good interaction  Conclusions

TAPPI 03 / G. Schubert 14.05.2003

1 Cold Rolling of Aluminium Foil

Cold rolling Doubling Cold rolling

Separating and Slitting Annealing

TAPPI 03 / G. Schubert 14.05.2003

Precipitations and Grain Structure in Non-Annealed and Annealed Foil

Grains Precipitations

Precipitations, also close to the surface

TAPPI 03 / G. Schubert 14.05.2003

2 Coil during annealing

TAPPI 03 / G. Schubert 14.05.2003

Oxide Growth during Annealing and Precipitations Embedded in the Surface

Oxide layers formed in a humid environment After annealing at room temperature

P P

P Oxide growth P interface

P = Precipitation (like AlFeSi, Al3Fe) T = Top layer B = Barrier layer

TAPPI 03 / G. Schubert 14.05.2003

3 Contact Corrosion Analogon in the Presence of Electrolyte

Electron conductivity Electrolyte

Oxide P

Al P

- -

e Cathode: ½ O2 + H2O + 2 e → 2 OH

t

y l - - o 2 H O + 2 e → 2 OH + H ↑ r 2 2

t

c

e

l 3+ - Cathode Anode Anode: Al → Al + 3 e

E Al 3+ + 3 OH- → Al(OH) ↓ Ion conductivity 3

also: Al + 2 H2O → AlO(OH) ↓+ ½ H2 ↑ Reactions depend on the availability of oxygen and water,

OK-167.cdr pH and temperature TAPPIG. Schubert 03 / G. Schubert 17.03.03 14.05.2003

Oxide Thickness by IR-Absorption

Edge

Base line offset Extinction

Centre

Wave number [cm-1] TAPPI 03 / G. Schubert 14.05.2003

4 Non-Wettable Width of a Foil Web

Wettable “Non-wettable“ Wettable

TAPPI 03 / G. Schubert 14.05.2003

Surface Tension and Wettability Categories for Aluminium Foil (AFCO) A: Water 100% 72.0 mN/m

B: Water/Ethyl alcohol 90% : 10% 47.0 mN/m

C: Water/Ethyl alcohol 80% : 20% 38.5 mN/m

D: Water/Ethyl alcohol 70% : 30% 33.0 mN/m m3

A B C D

8070 60 50 40 30 Categories of foil wettability [mN/m]

0K-163.cdr 26.11.2002 TAPPIG. Sc hub ert03 / G. Schubert 14.05.2003

5 Oxide Thickness and Wettability Profile

“Non-wettable“ width

]

]

°

[

m Oxide thickness, Water contact angle

n

e

[ l

annealed g

s

n

s

a

e

t

n

c

k

a

c

t

i

n

h

t

o

c

e

r

d

i

e

x t

a

O

W Oxide thickness, non-annealed

Distance from left edge [cm]

TAPPI 03 / G. Schubert 14.05.2003

Foil Annealing Requirements

— Recrystallising grain structure — Removing rolling oil — Maintaining good unwinding properties — Providing homogeneous wettability — Providing strong adhesion

TAPPI 03 / G. Schubert 14.05.2003

6 Permeants and Conditions Potentially Affecting Aluminium - Plastic Adhesion

Oxygen Water Acetic acid Citric acid Lactic acid Vitamin C Preservatives Fat Plastic Emulsifiers Salt Hot filling ? Pasteurising

Retorting Aluminium Storage time Light

OK-167.cdr TAPPIG. Schubert 03 / G. Schubert 17.03.03 14.05.2003

Permeation Measurements of Dairy Lid Coatings Oxygen or water vapour

Al removed

Coex or lacquer film Dairy cup with sealant N2-purging or exposed (Al removed) drying agent Lacquer Coex-coating (5 µm) (20 µm)

WVTR [g/d·m²] @ 20°C/ 100%r.h. 30 5

OTR [ml/d·m²·bar] @ 23°C/75% r.F. 380 7000 TAPPI 03 / G. Schubert 14.05.2003

7 Interaction Between Silanol and Alumina During Retorting

TAPPI 03 / G. Schubert 14.05.2003

Bubble Formation in a Retortable Stand-Up Pouch PET adh Al adh oPA adh PP 5050 µm µm

Adhesive remaining on PET

10 mm 100 µm

TAPPI 03 / G. Schubert 14.05.2003

8 Bubble Formation During Retorting

PET “dry spot“ with no adhesion Adhesive

Oxide Retorting P Al R e to rt in g

Adhesive Delamination

Oxide P Al

OK-166.cdr TAPPIG. Schubert 03 / G. Schubert 17.03.03 14.05.2003

“Dry Spots“ With No Adhesion and Oxide Layer Spots Grown in a Bubble

“Dry spot“ without adhesion PET (before retorting)

Al

20 µm Oxide spots grown during retorting

2 µm 2 µm

TAPPI 03 / G. Schubert 14.05.2003

9 Temperature Dependence of Permeation Through Plastics 10000

] Extrapolated trends for

d

? g

·

² permeation

n

i

t

m

r / 1000

o

m t

e

m

· PE starts R

g

[

melting t 100

n

e

i

c

i

f

f e Polymer / permeant o 10

c

n LDPE / acetic acid

o

i

t

a LDPE / n-decane e 1

m

r PP / n-decane

e P HDPE / n-decane 0,1 0 20 40 60 80 100 120 140 TAPPI 03 / G. Schubert Temperature [°C] 14.05.2003

Bond Formation of Acid Copolymers on Aluminium Foil

Hydrogen bond Soap

Oxide Top layer Barrier layer Metal TAPPI 03 / G. Schubert 14.05.2003

10 Fat Absorbed in a Sealant Coating After Retorting (IR)

During retorting in Glycerides Fatty acids contact with 0.070 --- Only water 0.060

0.050 --- Low fat content High fat content 0.040 --- High fat content Extinction 0.030 Low fat content Penetration depth for IR-ATR 0.020 No fat 3 µm 0.010 Coating

0.000 Tie 1600 1900 1800 1700 Metal 1650 Wave number (cm-1) TAPPI 03 / G. Schubert 14.05.2003

Plastification of Coatings During Retorting

SEM (no fat)*

SEM (high fat)* (* specimen extracted)

TAPPI 03 / G. Schubert 14.05.2003

11 Delaminations During Retorting

Film from the smooth-walled Glossy aluminium container, forming surface a pouch

Coating film

Packaged good: Simulant paste with fat and fatty acid TAPPI 03 / G. Schubert 14.05.2003

Species at a Delaminated Aluminium- Plastic Interface after Retorting

Retorting in Penetration depth contact with for IR-ATR --- Water 0.10 --- Low fat content Tie resin‘s --- High fat content C=O bonds 0.08

Triglyceride l

a

t

p

e 0.06 e

i Fatty acid o

T M

T Extinction 0.04 Al-soaps

0.02

0.00

1900 1800 1700 1600 Wave number [cm-1] TAPPI 03 / G. Schubert 14.05.2003

12 Abrasion Proofness and Bonding of Soap Species to the Aluminium Surface

IR-ATR on the metal 0.10 Before rubbing/washing the surface 0.08

l

0.06 a

t

p

e

e

i

o

T M T After rubbing/washing 0.04 Extinction the surface Tie resin‘s 0.02 C=O bonds

0.00

1800 1700 1600 Wave number [cm-1] Aluminium soaps adhere well to the metal surface ! TAPPI 03 / G. Schubert 14.05.2003

Adhesion Failure as a Result of Saponification

O O O O O C O OC CO CO O O O C O O C OC CO CO O OH

CO= O O O C O O C C=O O O C=O C C O O O C=O C OH OH O OH C OH O C=O CO= C=O C=O OH C=O OH C=O C=O C=O OH OH OH OH OH OH O O OH CO= OH OH O O CO= OH CO= C C CO= O CO CO= C=O C=O C=O O=C O=C C=O O=C O=C C=O OH C=O O O O O O O O-H O O O HO - Al - O - Al - O - Al - O - Al HO - Al - O - Al - O - Al HO - Al - O - Al - O - Al - O - Al Oxide Top layer O O O O Barrier layer Metal

TAPPI 03 / G. Schubert 14.05.2003

13 Migrated C=O-Species in the Adhering Interface of Different Tie Resins

0.12 Glycerides Tie resin‘s --- PP blend 0.11 C=O bonds 0.10 --- PP 0.09 --- PP/Copo blend 0.08 Fatty acids Epoxy 0.07 --- 0.06 Penetration depth

Extinction 0.05 for IR-ATR 0.04 0.03 0.02 0.01

l

a

t 0.00 p e

e

i

o

T

T 1800 1750 1700 M 1650 -1 TAPPI 03 / G. Schubert Wave number (cm ) 14.05.2003

Conclusions

— The surface of aluminium foil is well-prepared for adhesion, chemical resistance and acts as a barrier

— Complete spreading of coatings on foil is essential for durability

— Adhesion to foil can be affected by extreme migration during thermal treatment

— Under these conditions plastics are not as dense as expected and allow such migration

— Particular foil applications need a “smart“ functional barrier in the coating

TAPPI 03 / G. Schubert 14.05.2003

14